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Title: STREAM FLOW SIMULATION FOR THE UPPER AWASH BASIN
Authors: Shimelis Behailu
Advisors: Dr.Ing. Abdulkarim H. Seid.
Keywords: Key words: Awash, calibration, DEM, FEWS-SFM, flood, Koka, rainfall runoff,simulation, verification.
Copyright: 2004
Date Added: 15-Oct-2008
Publisher: Addis Ababa University
Abstract: Abstract The Awash Basin is the most utilized and most developed basin in Ethiopia. After the construction of the Koka dam the feature of the basin is changed in large extent. Heavy rainfall in the upstream catchments causes large inflow discharges to Koka Lake. At times where the water level is already close to the maximum water level, the excess water must be discharged through the spillways in order to prevent overtopping of the dam. The discharge through the spillway, together with the water discharged through the power plant turbines, has in the past caused flooding in the downstream areas, most notably in August 1996. To prevent the downstream areas from flooding, the water level in the lake could be lowered in advance provided the inflows could be forecasted. For this reason, the FEWS-SFM was calibrated for the Upper Awash Basin using five years (1991-1995) of stream flow and rainfall records. The model was verified using another five years data (1996-2000). Ground observed data were used for the calibration for both the physical characteristics of the basin and the dynamic inputs: rainfall and potential evapotranspiration. Simulation was done in three scenarios of defining the basin. First the basin is defined to have a single outlet at Melka Hombole hydrologic station. The second scenario divided the basin into six subbasins and the last scenario is made by dividing the catchment to thirty five subbasins. It is seen that the second scenario represented the rainfall runoff to an acceptable range both visually and statistically. The Nash and Sutcliff goodness of criteria (R2) was used for testing the model performance. R2 = 0.63 was obtained for the calibration and the verification yield R2 = 0.6. The simulation of the basin has underestimated the peak summer (July – August) and overestimated flow from March to June. The dry period flow is underestimated. However, further refinement of the DEM and investigation on the DEM and investigation on the way soil properties influencing the rainfall runoff process in the model may improve the model main rainy period flow and overestimation of the small rainfall period. From the results obtained further investigation on the way soil properties influencing the rainfall runoff process in the model is necessary.
Description: A thesis submitted to School of Graduate Studies, Addis Ababa University in partial fulfillment for the Degree of Masters of Science in Civil Engineering
URI: http://hdl.handle.net/123456789/1424
Appears in:ILS Proceedings - The 19th Annual Conference

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